Add topic support (#3711)

* add topic models and unit tests

* fix comments

* fix comment

* add the UI to show or add topics for a repo

* show topics on repositories list

* fix test

* don't show manage topics link when no permission

* use green basic as topic label

* fix topic label color

* remove trace content

* remove debug function

models/topic_test.go

@@ -0,0 +1,57 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package models
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAddTopic(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+
+	topics, err := FindTopics(&FindTopicOptions{})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 3, len(topics))
+
+	topics, err = FindTopics(&FindTopicOptions{
+		Limit: 2,
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 2, len(topics))
+
+	topics, err = FindTopics(&FindTopicOptions{
+		RepoID: 1,
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 3, len(topics))
+
+	assert.NoError(t, SaveTopics(2, "golang"))
+	topics, err = FindTopics(&FindTopicOptions{})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 3, len(topics))
+
+	topics, err = FindTopics(&FindTopicOptions{
+		RepoID: 2,
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 1, len(topics))
+
+	assert.NoError(t, SaveTopics(2, "golang", "gitea"))
+	topic, err := GetTopicByName("gitea")
+	assert.NoError(t, err)
+	assert.EqualValues(t, 1, topic.RepoCount)
+
+	topics, err = FindTopics(&FindTopicOptions{})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 4, len(topics))
+
+	topics, err = FindTopics(&FindTopicOptions{
+		RepoID: 2,
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 2, len(topics))
+}